1. Field of the Invention
The present invention relates to an inerting method for preventing fire and for extinguishing fire in an enclosed space, particularly a laboratory area, wherein fresh air is supplied in regulated manner to the compartment atmosphere as supply air and exhaust air is discharged from the compartment atmosphere in regulated manner, and wherein should a fire occur or to prevent a fire, the compartment atmosphere is fed an extinguishing agent which is gaseous under normal conditions as the supply air. The invention further relates to a device for extinguishing a fire which has broken out in an enclosed space, wherein the device includes at least one mechanism for providing an extinguishing agent which is gaseous under normal conditions and for immediately introducing said gaseous extinguishing agent into the compartment atmosphere of the enclosed space when a fire has broken out in said enclosed space.
2. Description of the Related Art
Supplying the compartment atmosphere of an enclosed space with an extinguishing agent which is gaseous under normal conditions in the event of a fire or to prevent a fire is known in the field of fire-fighting technology. For example, a system (method and device) for extinguishing fires in enclosed spaces is described in the DE 198 11 851 A1 document. In this conventional system, subject to a fire detection signal, an oxygen-displacing extinguishing agent which is gaseous under normal conditions (hereinafter referred to simply as “inert gas”) is introduced suddenly into the compartment atmosphere of the enclosed space; i.e., within the shortest possible time frame. The introduction of the inert gas lowers the oxygen content in the compartment atmosphere to a specific predefinable “inertization level.” This inertization level corresponds to a reduced oxygen content at which the inflammability of the goods or materials stored in the space is already lowered to the point that they can no longer ignite, thus, a fire which has already broken out will be smothered.
The extinguishing effect resulting from flooding an enclosed space with inert gas is based on the principle of oxygen displacement. As is generally known, “normal” ambient air consists of 21% oxygen by volume, 78% nitrogen by volume and 1% by volume of other gases. For extinguishing purposes or also as a preventative method to protect against fire, the percentage of oxygen in the compartment atmosphere of the area at issue is reduced by introducing an inert gas. An extinguishing or fire preventing effect is known to occur when the percentage of oxygen in the compartment atmosphere falls below a so-called “re-ignition prevention level.” The re-ignition prevention level is an inertization level which corresponds to a reduced oxygen concentration at which the goods or materials stored in the area at issue can no longer ignite and/or burn. Accordingly, the re-ignition prevention level, which is usually determined experimentally, depends on the fire load of the area to be protected. The oxygen percentage corresponding to the re-ignition prevention level is usually in a range of between 12% to 15% by volume. In the case of highly flammable matter, for example volatile solvents, however, the oxygen percentage corresponding to the re-ignition prevention level can even be lower than 12% by volume.
According to a guideline just recently issued by the Verband der Sachversicherer (VdS; “Property Insurer's Association”), when an enclosed space (“protected area”) is flooded, the oxygen concentration in the protected area should reach the re-ignition prevention level within the first 60 seconds of said flooding having been started. This thereby allows effective fire control with inert gas technology so that a fire in the protected area can be completely extinguished within the fire control phase.
In order to meet these requirements, it is necessary, particularly in large-volume areas such as laboratory spaces, production areas or warehouses, to be able to introduce a sufficient volume of inert gas into the compartment atmosphere of the enclosed space as quickly as possible when needed; i.e., within the 60 seconds stipulated by the VdS guideline.
Storing the oxygen-displacing gas used in the inert gas extinguishing method compressed into gas bottles for example lends itself well to this. Alternatively or additionally thereto, it is conceivable to provide for a device to produce an oxygen-displacing gas, for instance a so-called “nitrogen generator,” wherein the volume of gas produced by the device per unit of time does however need to be adapted commensurate to the volume of the protected area. This holds especially true when no other inert gas source is provided additionally to the nitrogen generator. When needed, the available volume of inert gas is then piped into the space at issue as quickly as possible, for example through a system of pipes having the corresponding outlet nozzles.
Due to the requirement of the inert gas extinguishing method needing to introduce an oxygen-displacing gas as quickly as possible into the enclosed space, at least at the start of the flooding, in order to render safe and effective fire control, it is essential to structurally provide for pressure relief for the enclosed space in order to prevent damage to at least parts of the shell enclosing the space. Such pressure relief is usually realized by installing pressure relief flaps. The function of pressure relief flaps is to protect the shell of the enclosed space from damage, even when the internal pressure within the space increases relatively quickly, for example due to the sudden introduction of a gaseous extinguishing agent. It is frequently provided to design the pressure relief flaps such that they will open automatically upon an empirically-predefined excess pressure. Opening the pressure relief flaps creates an opening in the shell of the enclosed space through which the excess pressure built up inside the space can escape. It is known for the pressure relief flaps to close again automatically after the excess pressure has been released; i.e., after the pressure has been relieved. To technically realize this self-opening and self-closing of the pressure relief flaps, it is known to use a mechanism with spring-loaded pins.
The disadvantage of this type of mechanical pressure relief can be seen in that the space needed to be provided for same must be estimated in the early planning stage, prior to the structural completion of the enclosed space. The dimensions to the pressure relief flaps to be installed moreover have to be determined in the early planning stage. Particularly needing to be estimated in advance is what the effective area for the air or gas opening provided by the pressure relief flaps will be.
In designing and dimensioning the pressure relief flaps to be employed, conventional approaches often assume a theoretical high pressure which might develop within the enclosed space. For reasons of planning reliability, this theoretical value often needs an additional more or less generous safety margin in order to allow for unplanned pressure loads. Yet installing oversized pressure relief flaps is disadvantageous in terms of cost.
Moreover, it is often the case that an enclosed space which is already equipped with a conventional inert gas fire extinguishing system can only be remodeled or expanded to a limited degree. For example, when restructuring makes structural measures necessary in order to enlarge the volume of the space, additional pressure relief flaps may need to be provided so as to allow for mandatory safety-related requirements.
Nor does the previously-known approach for providing pressure relief allow, or only allows at great structural expense, an artificial pressure ratio intentionally set in the compartment atmosphere prior to the flooding with inert gas to be maintained during the flooding in the case of areas which are already equipped with conventional inert gas fire extinguishing systems and conventional pressure relief. This requirement is for example to be considered in the case of laboratory areas of permanently-reduced compartment pressure compared to the ambient pressure in which lower pressure is set within the area in order to prevent the escape of particles, substances, viruses, etc., with the potential to pose a health hazard. This protective measure afforded by the permanently-set negative pressure would fail if conventional mechanical pressure relief flaps which open outward as needed were used to relieve pressure.